Semiconductor uses solar power to take H2 from water

In what is being touted as ''artificial photosynthesis,'' researchers at the Ecole Polytechnique Federale de Lausanne (EPFL) have devised a technique for coating a cuprous oxide semiconductor so that it can use energy from the sun to take hydrogen from water.

Adriana Paracchino and Elijah Thimsen have engineered photoelectrochemical cells that, when exposed to sunlight, can provide the current needed to drive the chemical reactions that separate hydrogen gas (H2) from water.

At the simplest level, imagine a piece of something, say a spoon, in a glass of water out in the sun. The idea is that the sunlight will hit the spoon which will in turn cause a reaction so that the water molecules will be split, producing hydrogen (H2 gas, a useful way to store energy that can easily be used as fuel) and oxygen.

But of course in real life it isn't that simple. That hypothetical illustration will, in reality, just cause the water to evaporate.

So the ''spoon'' needs to be a special spoon that can use energy from the sun that will, instead of making the water molecules evaporate, make the water molecules split - that is, undergo a chemical reaction. This chemical reaction can be achieved using an electric current.

Cuprous oxide (Cu2O), can be used to make that special spoon. It is commonly used in paint and fungicide, and is one of the most studied semiconductors around. It has been known to be photosensitive since 1904. It is also inexpensive and abundant, perfect for a potential silver bullet (errr- silver spoon) for the energy crisis.

However, when Cu2O isexposed to water and light, it breaks down and loses it's ability to act as the magic spoon. So Paracchino and Thimsen covered Cu2O with atom-thin layers of zinc oxide and titanium oxide using a technique called atomic layer deposition (ALD) that is commonly used for making memory chips for laptop computers and other electronic devices.

With the protective layer in place, the Cu2O can harness solar energy and convert it to an electric current that can drive the chemical reactions to make H2 separate from water.

Pretty cool. The research ''Highly active oxide photocathode for photoelectrochemical water reduction'' is published in the May issue of Nature Materials. News report interpreting the paper say that the next step is to improve the the electrical properties of the protective layer. They also note that the materials used are widely available and the techniques can easily be scaled up for mass production.

If this alternative energy technology can be made to work on a large scale soon, it could be the answer to the nuclear energy dilemma.

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